Separation of acidic constituents from gases



June 10, 1952 F. c. RIESENFELD EIAL 2,600,328

I SEPARATION ACIDIC CONSTITUENTS FROM GASES Filedvuxm 7, 1948 Jaw/ewe F'eED C Bess-MP2; o,

.HENQY D; .FAz/ee,

INVENTORS.

Patented June 10, 1952 SEPARATION OF ACIDIC CONSTITUENTS FROM GASES Fred C. Riesenfeld, Hollywood, and Henry D. Frazier, Alhambra, Calif., assignors to The Fluor Corporation, Ltd., Los Angeles, Calif., a

corporation of California Application June 7, 1948, Serial No. 31,484

7 Claims.

This invention has to do with the separation of weakly acidic constituents, such as hydrogen sulfide and carbon dioxide, from hydrocarbon or other gases, and is directed particularly to an improved process for selective dissolution of reaction compounds of such constituents, whereby they may be removed from the gas and then separately recovered, all in a continuous absorp tive and regenerative cycle.

The invention is especially concerned with the removal of hydrogen sulfide and carbon dioxide from hydrocarbon gases, and contemplates generally the treatment of the gas with an absorbent reactive with the carbon dioxide and hydrogen sulfide, and having then a two liquid phase composition, the individual phases respectively containing absorbed carbon dioxide and hydrogen sulfide. These phases then are separable and capable of individual regeneration to separately release their absorbed acid gases.

We have discovered that solutions containing an aliphatic amine, preferably an alkanolamine, water and a, third component compatible or miscible with both, will dissolve the reaction prodnets of the amine with hydrogen sulfide, without however retaining in homogenous solution appreciable quantities of the reaction products of the amine with carbon dioxide. In other words, reaction of the amine and carbon dioxide results in formation of a carbamate which, by virtue of the presence of the aforesaid third component, is rendered separable because of limited solubility of the carbamate in the remaining solution. Accordingly, as such solutions become saturated with carbon dioxide and hydrogen sulfide, they form into two phases separable as upper and lower layers, the former of which contains most of the combined hydrogen sulfide and no appreciable combined carbon dioxide, while the lower layer contains substantially all of the combined carbon dioxide (i. e. carbamate) and some hydrogen sulfide-amine reaction product. The reaction and phase separation effect appears to be that upon reaction with carbon dioxiode, the amine in the initial treating solution separates into the lower phase, and progressively as the reaction occurs because of the substantial insolubility of the reaction product in the upper phase. Thus, upon regeneration, the so-called upper phase releases substantially pure hydrogen sulfide, while the lower phase gives off a substantial quantity of the carbon dioxide content of the treated gas, with perhaps some hydrogen sulfide.

The amine component of the treating solution may be any of the alkanolamines or aliphatic amines known to be reactive with acid gases, see Hutchinson Patent 2,177,068.

The followingclasses of compounds are found to be suitable diluents or additives solublein water-amine solutions, the diluent in any instance preferably having a boiling temperature in excess of about 190 C.: Monohydric alcohols, water soluble monoethers of polyhydric alcohols (such as carbitols and Cellosolves and particularly butyl carbitol, butyl Cellosolve and phenyl Cellosolve), and water soluble multiple ethers of polyhydric alcohols such as dimethoxy tetraglycol. In some instances, though not necessarily in all cases, it may be desirable to include a glycol, typically diethylene glycol, in the solution as for the purpose of aiding in maintenance of the amine-hydrogen sulfide reaction product in a condition more completely confined to the upper layer or phase.

The following are cited as typical treating solutions:

Example 1 20% Monoethanolamine 10% Water 70% Butyl carbitol Example 2 30 Triethylenetetramine 25% Thio-glycol 35% Carbltol 10% Water Example 3 1'7 Monoethanolamlne 46% Methyl Cellosolve acetate 32% Diethylene glycol 5% Water Example 4 30% Diethylenetriamine 30 Carbltol 35% Diethylene glycol 5 Water lower hydrogen sulfide content than the quantities of carbon dioxide, hydrogen sulfide and perhaps also some moisture, which incidentally may also be removed, particularly where a hygroscopic diluent such as diethylene glycol is included in the absorbent solution. The sour gas is fed through line It to a contactor column H through which the gas flows upwardly and in intimate contact with a down-flowing stream of regenerated solution introduced to the column through line l2. The treated gas leaves the contactor through line !3. The rich solution, containing absorbed hydrogen sulfide and carbon dioxide, is discharged through line it to a separator it within which the solution stratifies. Merely as illustrative, the solution may convert to an upper layer or stratum containing the absorbed hydrogen sulfide, and practically nocarbon dioxide, and a lower stratum containing carbon dioxide and a relatively small quantity of hydrogen sulfide. v

The-upper stratum is discharged from the separator through line it and exchanger I! into a still 18 suitably supplied with heat, as by the conventional reboiler 19. Upon being heated in the still, the solution is stripped of its hydrogen sulfide content, the latter being recoverable from line 20 as high purity hydrogen sulfide. The stripped solution then is returned from the still or reboiler through line 2|, exchanger IT and cooler 22, for recirculation through the con t actor;

Thelower liquid stratum in separator 15 is discharged through line 23 and exchanger 2:? into a second still 25 receiving bottom heat from reboiler 26 at a temperature suificient for regeneration of the solution; The absorbed acid gas, for the most part carbon dioxide, is released from the column for further dispositionthrough line 21. The lean solution is recirculated through line 28, exchanger 2 3- and cooler 22, for admixture with the solution being returned from line 2|. Being mutually soluble or compatible, the two solutions when introduced together to the contactor, or admixed therein according. to the variation described below, constitute a single phase absorbent solution.

In Fig. 2 we illustrate a variation of the described system, by means of which it is possible to more completely absorb hydrogen sulfide from the gas, to effect greater dehydration, and if desired, to lower steam requirements for stripping. This variational flow cycle is similar to the described system except that the regenerated solution leaving reboiler 28 through exchanger 24 and line 28, is passed through" a cooler 29, beyond which all or a portion of the solution is introduced through line 30 into the topof the contactor. The regenerated solution leaving reboiler l9 and flowing through line 2| and exchanger l'l, is passed through cooler 3i and returned to the contactor ll through line 32 at a point several trays below the top tray of the contactor, either alone or mixed with a portion of the solution takenfrom line 30 through line Wander-control ofa suitable regulator or valve Considering the differences in compositions, particularly with reference to hydrogen sulfide, of the solutions in the stills l8 and 25, it will be appreciated that with its initially lower hydroefiect of its absorbed carbon dioxide, the solutioninstill .25 can more easily be stripped to a w y solution being stripped in still i8? Accordingly, by selec- .gen'sulfide content and aided by the stripping tively introducing the lean solution from line 28 to the top of the contactor, advantage is taken of the relatively greater purity of this solution in respect of hydrogen sulfide contamination, as a means of effecting more complete hydrogen sulfide absorption in the top trays of the contactor, and therefore greater purity of the treated gas.

Dehydration of the gas is improved for the reason that as concentrated in the shell 25, the lean solution can be made highly hygroscopic by reason of the moisture absorptive properties of the amine in the presence of low Water content and the third non-aqueous component or diluent.

Reduction of required total stripping steam is made possible because of permissible incomplete stripping of hydrogen sulfide in the still it, made possible by the fact that the lean solution taken from the still is introduced to the contactor below its top trays, and at a location where the presence of appreciable hydrogen sulfide in the solution will not impair the purity of the treated gas as determined by the top tray liquid compositions.

We claim:

1. The method of treating a hydrocarbon gas containing hydrogen sulfide and carbon dioxide,

that includes contacting the gas in a contacting zone with a monophase liquid absorbent solution comprising an alkanolamine, water and a compound having a boiling temperatureabove 196 C. and of the groupconsisting of monohydric alcohols, water soluble ethers of polyhydric alcohols, and water soluble" multiple ethers of polyhydricalcohols, in sufficiently high concentration of said compound to cause by reaction of the amine with said hydrogen sulfide and carbon dioxide, the formation of two liquid phases one containing the bulk of, the aminecarbon dioxide reaction product and the other the buil of the amine-hydrogen sulfide reaction product by" virtue of the relative insolubility of the air ine-ca'rbon dioxide reaction product in theremainder' of the solution, separately heating and stripping said phases of jtheir absorbed gases and returning the stripped liquids to i said conia'cti'rigzon'e. v

2. The method claimed in claim 1, in which said monophase solution contains also a glycol.

3. Themethod of treating a hydrocarbon gas containinghydrogen. sulfide and" carbon dioxide, that includes contacting the gas in a contacting zone with'a monophase liquid absorbent solution comprising'an' alkanolamine; water and a: water soluble ether of' a polyhydric'j alcohol having a boiling temperature in XCeSS'. 0f19 0C., thereby reacting the] amine with said hydrogen sulfide and carbon dioxide the formation" of twoliquidphases one containing the bull; of. the aminecarbon dioxide reaction product and the other the bull: of the amine-hydrogensulfid reaction product by'virtue of the relative'insolubility of the amine-carbon dioxide reaction product in the remainder of the solution, separately heating and stripping said phases of their absorbed gases and returning the stripped liquidfto' said contacting" zone.

l. The method claimed in claim 3, in which said monophase solution contains alsoa glycol.

5. The method of; treating a hydroicarb'ongas containing hydrogen sulfide and carbondioxide, that includes contactingv the gas in a contacting zone with a monophase liquid absorbent solution comprising an alkanolamine, water and acompound having. a boiling temperature" above C; and o'i'the' group consistmgof" monohydric alcohols, water soluble ethers of polyhydric alcohols, and water soluble multiple ethers of polyhydric alcohols, in sufficiently high concentration of said compound to cause by reaction of the amine with said hydrogen sulfide and carbon dioxide the formation of two liquid phases one containing the bulk of the amine-carbon dioxide reaction product and the other the bulk of the amine-hydrogen sulfide reaction product by virtue of the relative insolubility of the amine-carbon dioxide reaction product in the remainder of the solution, separately heating and stripping said phases of their absorbed gases and returning the liquids constituting the hydrogen sulfide and carbon dioxide stripped phases respectively to relatively upper and lower locations in said contacting zone.

6. The method of treating a hydrocarbon gas containing hydrogen sulfide and carbon dioxide, that includes contacting the gas in a contacting zone with a monophase liquid absorbent solution comprising an alkanolamine, water and a compound having a boiling temperature above 190 C. and of the group consisting of monohydric alcohols, water soluble ethers of polyhydric alcohols, and water soluble multiple ethers of polyhydric alcohols in sufiiciently high concentration of said compound to cause by reaction of the amine with said hydrogen sulfide and carbon dioxide the formation of two liquid phases, passing the solution and reaction products into a separating zone wherein there is formed said liquid phases one containing the bulk of the amine-carbon dioxide reaction product and the other the bulk of the amine-hydrogen sulfide reaction product by virtue of the relative insolubility of the amine-carbon dioxide reaction product in the remainder of the solution, separately withdrawing and passing the hydrogen sulfide and carbon dioxide reaction product phases respectively through first and second separate heating zones, and returning the stripped liquids from said heating zone to said contacting zone.

7. The method of treating a hydrocarbon gas containing hydrogen sulfide and carbon dioxide,

that includes contacting the gas in a contacting zone with a monophase liquid absorbent solution comprising an alkanolamine, Water and a compound having a boiling temperature above C. and of the group consisting of monohydric alcohols, water soluble ethers of polyhydric alcohols, and water soluble multiple ethers of polyhydric alcohols in sufliciently high concentration of said compound to cause by reaction of the amine with said hydrogen sulfide and carbon dioxide, passing the solution and reaction products into a separating zone wherein there is formed said liquid phases one containing the bulk of the amine-carbon dioxide reaction prodnot and the other the bulk of the amine-hydrogen sulfide reaction product by virtue of the relative insolubility of the amine-carbon dioxide reaction product in the remainder of the solution, separately withdrawing and passing the hydrogen sulfide and carbon dioxide reaction product phases respectively through first and second separate heating zones, returning the liquid from said first heating zone to the top of the contacting zone and returning the liquid from said second heating zone to a lower location in the contacting zone.

FRED C. RESENFELD. HENRY D. FRAZIER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,086,732 Millar et a1. July 13, 1987 2,139,375 Millar et a1. Dec. 6, 1938 2,143,393 Ulrich et a1. Jan. 10, 1939 2,161,663 Baehr et al. June 6, 1939 2,177,068 Hutchinson Oct. 24, 1939 2,399,142 Reed Apr. 23, 1946 2,437,288 Anderson Mar. 9, 1948 2,445,468 Blohm et a1. July 20, 1948 2,550,446 Blohm et al. Apr. 24, 1951 

1. THE METHOD OF TREATING A HYDROCARBON GAS CONTAINING HYDROGEN SULFIDE AND A CARBON DIOXIDE, THAT INCLUDES CONTACTING THE GAS IN A CONTACTING ZONE WITH A MONOPHASE LIQUID ABSORBENT SOLUTION COMPRISING AN ALKANOLAMINE, WATER AND A COMPOUND HAVING A BOILING TEMPERATURE ABOVE 190* C. AND OF THE GROUP CONSISTING OF MONOHYDRIC ALCOHOLS, WATER SOLUBLE ETHERS OF POLYHYDRIC ALCOHOLS, AND WATER SOLUBLE MULTIPLE ETHERS OF POLYHDRIC ALCOHOLS, IN SUFFICIENTLY HIGH CONCENTRATION OF SAID COMPOUND TO CAUSE BY REACTION OF THE AMINE WITH SAID HYDROGEN SULFIDE AND CARBON DIOXIDE, THE FORMATION OF TWO LIQUID PHASE ONE CONTAINING THE BULK OF THE AMINECARBON DIOXIDE REACTION PRODUCT AND THE OTHER THE BULK OF THE AMINE-HYDROGEN SULFIDE REACTION PRODUCT BY VIRTUE OF THE RELATIVE INSOLUBILITY OF THE AMINE-CARBON DIOXIDE REACTION PRODUCT IN THE REMAINDER OF THE SOLUTION, SEPARATELY HEATING AND STRIPPING SAID PHASES OF THEIR ABSORBED GASES AND RETURNING THE STRIPPED LIQUIDS TO SAID CONTACTING ZONE. 